What is Koji Fungus?

Koji(Aspergillus oryzae) is often called moyashi(bean sprouts) in the sake industry, because of its appearance when viewed under a microscope.Koji was named byHerman Ahlburg in 1876, who was a professor of medicine in Tokyo at the time.

Oryzae refers to the rice plant, Oryzae sativa, (cultivated / domesticated rice) so the close relationship between koji and rice is clear.

In Asian countries, alcoholic beverage are commonly produced using koji .The koji fungi are divided into two types: mochi koji and bara koji.Mochi koji which is normally propagated when dry,powdered rice and other crops are mixed with water.It is called mochi koji because the raw materials look like a block of sticky rice, called mochi in Japanese.

On the other hand, bara koji can propagate on steamed crops. As a prefix,bara means “separated “in Japanese.The fungus propagate on each single rice grain,so it is called bara koji.

Unlike mochi koji ,bara koji can dissolve thermal denaturated protein. Since koji fungus in general propagates by consuming amino acid (they can not eat protein), an additional process to convert protein to amino acid is needed. But mochi koji cannot dissolve the thermal denaturated protein of steamed rice, so they can not survive on the steamed rice.

Bara koji is a rarekoji(Normally mochi koji is used in the other Asian coutries)which brings to sake an unexampled production process which makes Japanese sake one of the unique alcoholic beverage in the world.